Optimization of spoiled gradient‐echo phase imaging for <i>in vivo</i> localization of a focused ultrasound beam

TLDR

The study optimized a spoiled gradient‑echo pulse sequence by selecting an echo time equal to twice the tissue T*2, the longest repetition time compatible with a 20‑s sonication, and a flip angle at the Ernst angle, and then measured temperature rise via proton resonance frequency shift and phase‑difference SNR in skeletal muscle and kidney cortex of 10 rabbits. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, corresponding to a temperature elevation of 7.3 °C, and localize the beam within one voxel (0.6 × 0.6 × 5 mm³) at power levels below the thermal damage threshold.

Abstract

Abstract The parameters of a spoiled gradient‐echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal‐to‐noise ratio (SNR δ ϕ ) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T * 2 of the tissue, the longest repetition time possible with a 20‐s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3°C. The sonication beam can be localized within one voxel (0.6 × 0.6 × 5 mm 3 ) at power levels that are below the threshold for thermal damage of the tissue.